Ukrainian soldiers man a checkpoint near the village of Chongar, near a Crimea region border March 10.

Paris - French Foreign Minister Laurent Fabius warned Tuesday that sanctions against Russia could come as early as this week if Moscow does not respond to Western proposals to solve the crisis in Ukraine.

“If they respond positively (to the proposals), (US Secretary of State) John Kerry will go to Moscow, and then sanctions will not be immediate. If they do not respond or if they respond negatively, there will be a series of sanctions that could be taken as early as this week,” he said on France Inter radio.

Kerry sent Russia a series of proposals to try and de-escalate the crisis in Ukraine, where Kremlin-backed forces have seized the Crimea peninsula, which now plans to hold a referendum Sunday on switching the region's allegiance from Kiev to Moscow.

The proposals include setting up a contact group to bring together Ukraine and the Russia in formal talks.

But Russian Foreign Minister Sergei Lavrov said in a televised meeting Monday that the proposals “do not suit us very much”, adding Moscow would unveil its own solution to the crisis.

Fabius said the sanctions would involve “freezing personal assets of Russians or Ukrainians and sanctions on travel, regarding visas.”

He added that Sunday's referendum in Crimea is “illegal”.

Officials from the United States, Japan, Canada, Turkey and several EU countries were due to meet in London on Tuesday to discuss the issue of international sanctions.

“This is a technical, official-level meeting to ensure that we have a broad common understanding on what measures we are considering internationally,” a Foreign Office spokesman said.

On Monday, British Prime Minister David Cameron told lawmakers that the EU was looking at “further measures, the so-called second phase, which would need to start rapidly” if Russia failed to cooperate.

“These include asset freezes and travel bans,” he said.

In addition, “we are working closely with our American, European and other international partners to prepare a list of names, and these sanctions - plus the measures already agreed against Yanukovych and his circle - will be the focus of a meeting here in London tomorrow with key international partners.”